1. Field of the Invention
The present invention relates to a magnetoresistive (MR) effect transducer which can be used as a read head for sensing a leakage magnetic field from a magnetic medium.
2. Description of the Related Art
MR effect transducers are divided into a ferromagnetic tunneling junction (MTJ)-type and a spin valve type.
An MTJ structure of the MTJ-type MR effect transducer is constructed by a pinned ferromagnetic layer, a free ferromagnetic layer and a non-magnetic insulating layer sandwiched by the pinned ferromagnetic layer and the free ferromagnetic layer.
On the other hand, a spin valve structure of the spin valve type MR effect transducer is constructed by a pinned ferromagnetic layer, a free ferromagnetic layer and a non-magnetic conductive layer sandwiched by the pinned ferromagnetic layer and the free ferromagnetic layer.
In a prior art MTJ-type MR effect transducer (see JP-A-10-162327), longitudinal bias ferromagnetic layers are provided at the side of the MTJ structure to provide magnetic domain control over the free ferromagnetic layer, thus suppressing the Barkhausen noise. This will be explained later in detail.
On the other hand, in a prior art spin valve type MR effect transducer (see U.S. Pat. No. 5,668,688), longitudinal bias ferromagnetic layers are also provided at the side of the spin valve structure to provide magnetic domain control over the free ferromagnetic layer, thus suppressing the Barkhausen noise.
In the above-described prior art MR effect transducers, however, since the free ferromagnetic layer is separated from the longitudinal bias ferromagnetic layer by a magnetic isolation layer, it is difficult to apply a sufficiently large magnetic bias field to the free ferromagnetic layer, which would increase the noise in reproduced signals.
In addition, in the above-described prior art MR effect transducers, each layer of the MTJ or spin valve structure has the same pattern. Therefore, when the MTJ or spin valve structure is patterned by a milling process, metal particles or contamination may be adhered to the sides of the non-magnetic layer, so that the pinned ferromagnetic layer and the free ferromagnetic layer are short-circuited by the metal particles or contamination adhered to the sides of the non-magnetic layer. This would decrease the manufacturing yield of MR effect transducers.
It is an object of the present invention to improve the noise characteristics of MR effect transducers.
Another object of the present invention is to improve the manufacturing yield of MR effect transducers.
According to the present invention, in a magnetoresistive effect transducer including a pinning layer, a pinned layer, a free layer and a non-magnetic layer inserted between the pinned layer and the free layer, a longitudinal bias layer is connected directly to a part of the free layer to apply a bias magnetic field to the free layer, thus biasing a magnetization direction of the free layer so that the magnetization direction of the free layer coincides with that of the longitudinal bias layer. Thus, the noise characteristics are improved.
Also, an uppermost layer of the MTJ or spin valve is patterned by a milling process, so that the uppermost layer has a smaller pattern than the other layers. This would prevent metal particles or contamination from adhering to the non-magnetic layer, thus improving the manufacturing yield.